This invention relates to accelerator control systems for motor vehicles, and more particularly to accelerator control systems capable of providing throttle idle validation for electronic engine controls.
Electronic engine control systems typically employ some form of electrical or electronic sensor of accelerator pedal position, such as a potentiometer mechanically linked to the accelerator pedal such that its wiper output signal is a linear function of pedal position. Examples of the above are disclosed in the following patents:
______________________________________ Patent No. Inventor Issue Date ______________________________________ 4,534,328 Fischer et al. Aug. 13, 1985 4,597,049 Murakami Jun. 24, 1986 4,640,248 Stoltman Feb. 3, 1987 4,793,308 Brauninger et al. Dec. 27, 1988 4,849,896 Burk et al. Jul. 18, 1989 4,881,502 Kabasin Nov. 21 1989 4,979,117 Hattori et al. Dec. 18, 1990 ______________________________________
Redundancy is provided in some systems in the form of an idle switch, which provides an independent idle position indication in the event of failure of the primary pedal position sensor. Such a system is disclosed in a paper by Lannan et al. entitled "Cummins Electronic Controls for Heavy Duty Diesel Engines," IEEE 88 CH2533-8, presented at the International Congress on Transportation Electronics, Convergence 88, Dearborn, Mich., Oct. 17-18, 1988. An idle switch and a potentiometer are also disclosed in U.S. Pat. No. 4,979,117 to Hattori et al., cited above, as part of a failure detection system which additionally employs a second switch for indication of the wide-open position of the accelerator pedal. If the potentiometer output voltage is outside a predetermined range, the system according to that patent allows vehicle operation at a speed determined by the switch states, e.g., idle speed if the idle switch indicates that the accelerator pedal is in its idle position, and some predetermined value above idle speed if the idle switch indicates a non-idle state. The same system detects malfunctions of the switches by comparing their actual states with expected states when the position sensor produces a mid-range output signal. U.S. Pat. No. 4,597,049 to Murakami, cited above, also discloses a pedal switch in addition to a potentiometer, for the purpose of generating a timing pulse when the accelerator pedal is depressed to accelerate the vehicle.
Another failure detection technique involves the use of a force sensor such as a strain gauge for sensing the force applied to the accelerator pedal, and for maintaining the engine at idle when the force applied is zero. This type of system, illustrated in the above-referenced U.S. Pat. Nos. 4,640,248 and 4,881,502 to Stoltman and Kabasin, respectively, is designed to provide fail-safe operation in the event the accelerator pedal sticks in an off-idle position. As pointed out in the latter patent, a pedal force sensor produces a false indication of idle state when the vehicle is operating in cruise control mode.
A well known drawback of redundant systems is that they often introduce new failure modes. One approach for avoiding the effects of such failure modes is disclosed in U.S. Pat. No. 4,739,469 to Oshiage et al., wherein it is suggested that replacement of a main control circuit with a backup circuit be carried out only when the backup circuit outputs a unique switching signal, such as a particular signal at or near a predetermined frequency or alternatively a plurality of parallel logical signals in a predetermined combination.
Despite substantial activity in this area, there remains a need for improved techniques for detecting sensor failures, for example, in-range position sensor failures, idle switch failures and the like, without complex, expensive or unreliable sensors or circuits which may introduce further undesirable failure modes.